PROJECT SUMMARY/ABSTRACT Intercellular communication between fiber cells is critical for lens homeostasis and it is well established that gap junctions facilitate the diffusion of small molecules between adjacent fiber cells. Recently, however, we have obtained evidence that large molecules such as proteins can also diffuse between fiber cells. The conduits for intercellular protein diffusion may be regions of limited cell-cell fusion. The presence of fusions between cells in the lens core ensures that the central region of the lens functions as a syncytium. The physiological significance of the core syncytium is not known. Lim2 is the second most abundant integral membrane protein in the lens. It is a member of the claudin super- family and has putative adhesive functions in the lens. In preliminary experiments, the Lim2 locus was disrupted in mice by insertional mutagenesis, resulting in a functional null for Lim2. Significantly, in the absence of Lim2, the lens syncytium did not form. Furthermore, laser analysis of Lim2-null mouse lenses revealed that the internal refractive properties of the lens were profoundly disturbed. These observations suggest a link between the expression of a lens membrane protein (Lim2), syncytial organization, and refractive function in the lens. The current application will examine the molecular mechanism by which macromolecules diffuse between lens cells, the role of Lim2 in the formation of the lens syncytium, and the relationship between syncytial organization and the lens gradient refractive index (GRIN). These studies are expected to provide novel insights into the previously unsuspected link between intercellular diffusion of macromolecules and lens optical quality. This information will, in turn, inform our view of image formation in the eye and the role of the lens in the optical train. PROJECT NARRATIVE The role of the lens is to focus light sharply on the retina. This application will examine how the intercellular movement of protein within the lens contributes to its optical quality.